1. Technical Field
The present invention relates to a transfer apparatus and an image forming device.
2. Related Art
Heretofore, in image forming devices such as printers, copiers and the like, a transfer apparatus has been employed which sequentially primary-transfers and superposes toner images of respective colors onto an intermediate transfer belt, and secondary-transfers the superposed toner images from the intermediate transfer belt onto a recording medium.
However, a technical problem has been apparent in that when image formation is performed using an intermediate transfer belt with high electrical resistance, fish scale-like image defects (below referred to as “scale-form defects”) are formed in the image that has been transferred onto paper. The present inventors have investigated these image defects and have discovered that the scale-form defects arise in accordance with gap discharges that occur between the intermediate transfer belt and a backup roller at a pre-nipping region which is positioned immediately preceding a nipping region (a transfer nipping region) where the paper enters into between the intermediate transfer belt and the secondary transfer roller.
These gap discharges are positive discharges, and it is known that positive discharges form charge patterns with round scale shapes. A scale shaped charge pattern formed at the rear face of an intermediate transfer belt is more likely to be maintained when electrical resistance of the intermediate transfer belt is higher. Then, when the toner moves from the intermediate transfer belt to the paper, the scale shaped charge pattern at the rear face of the belt takes effect, and a scale pattern is formed on the paper.
In particular, when a “spherical toner” with high transfer efficiency is employed as the toner, to the extent that adhesion force of the toner is lower, the toner is more easily detached from the intermediate transfer belt by weak discharges. Consequently, the scale-form defects are more likely to occur.